I did some looking around and found there were so many misdemeanors for this infamous airlines, such as: one 1990, another one from 2006, and obviously the recent one
The pilots didn't answer radio calls for more than an hour. It scared the air traffic controllers so badly that a military plane was standing by to intercept the airliner.
One can argue, at a time of so much discussion about the problem of pilot fatigue, whether the Federal Aviation Administration should still require pilots to stay awake at all times during U.S. flights. Many international carriers permit naps.
Now you can invent new usages for the phrase such as, Last night the old train station burned down while the cops parked down the block from it were taking a Northwest Nap.
"Urban Dictionary: Northwest Nap - A very deep sleep where you are unable to hear telephones, text messages and even the Air Force. As in, Dude, I was so tired yesterday, I took a Northwest Nap. My girl called me 15 times and I didn't hear a thing!"

